The correct answer is investigate.
The correct answer is (C) To investigate. To search, as if burrowing; to perform thorough research (of documents, for data or information, etc.). Also, to dig, as with a spade; to excavate; to obtain by digging.
Delve comes from Middle English delven, Old English delfan (to dig).
Examples of use:
- She immediately delved into the problem.
- He intended to delve into all possible sources during his search.